1. Field of the Invention
The present invention relates to methods of repairing nozzles made of Inconel 600 material and providing communication between the interiors of pressure vessels and externally thereof and, more particularly, to methods of repairing Inconel 600 nozzles of reactor vessels of pressurized water reactors.
2. Description of the Prior Art
Pressure vessels and, in particular, reactor vessels of pressurized water reactors, typically have one or more nozzles disposed along external boundaries or walls of the vessels to provide communication with the interiors of the vessels from externally thereof. The nozzles include tubes or sleeves that extend through apertures or bores in the external walls, the external walls providing an interface between the interiors of the vessels and the environment. The nozzles can extend beyond interior surfaces of the external walls to protrude into the interiors of the vessels or can be substantially flush with the interior surfaces for being secured to the vessels by welding along the interior surfaces. The nozzles extend externally of the vessels; and, accordingly, the nozzles form continuations or extensions of the external boundaries of the vessels with the lumens or passages of the nozzles providing access to the interiors of the vessels from externally thereof. Various diverse procedures can be performed via the nozzles in accordance with the specific characteristics and functions of the vessels, and various tools or instruments can be inserted into the interiors of the vessels through the nozzles for various different procedures. Some of the procedures or functions that can be performed with the nozzles include control rod drive penetration, heater penetration, pressure tap and measurement, thermowell and instrument line conduit. Because the nozzles form extensions of the external boundaries of the vessels, it is extremely important to prevent cracking of the nozzles and concomitant leakage through and around the nozzles so as not to break the interface between the vessel interiors and the environment. Although nozzles of the above-described type have been made of Inconel 600 material to resist degradation and cracking, walls of the nozzles in the areas of the welds remain susceptible to cracking due to weld stress, corrosion, service induced stress corrosion as well as other effects. When such cracks occur, leak paths are established through the walls of the nozzles, allowing fluid within the vessels to flow through the cracks and along the apertures or bores in the external walls of the vessels to penetrate the interface between the vessel interiors and the environment. Where the vessels contain radioactive fluids as in nuclear pressurized water reactors, leakage through and around the nozzles can result in radioactive water or steam contamination of areas where personnel are present and represents a significant problem. One way to repair cracked Inconel 600 nozzles is by welding; however, in many cases and, in particular, in nuclear pressurized water reactors, repair by welding results in numerous disadvantages including undesirably high radiation exposure for personnel, forced outage time and its attendant cost, and preparation and implementation costs. In nuclear pressurized water reactors, nozzle repair techniques are further limited by the unique requirements and conditions of nuclear power plants including high pressure hot water or steam service, the need for usability of the nozzles following repair and conformance with Nuclear Regulatory Commission Standards.
In the past, 304 stainless steel control rod drive penetration nozzles of reactor vessels of nuclear boiling water reactors have been repaired by rolling inside diameter surfaces of the nozzles. The 304 stainless steel control rod drive penetration nozzles repaired by rolling were not welded directly to the external walls of the reactor vessels but, rather, to 304 stainless steel stub tubes concentrically receiving portions of the nozzles protruding beyond the interior surfaces of the external walls. The stub tubes in turn were welded to the reactor vessels along the interior surfaces of the external walls, with the nozzles extending externally of the vessels through apertures or bores in the external walls. The walls of the stub tubes cracked in the vicinity of the welds securing the stub tubes to the external walls, allowing fluids in the vessels to flow through the cracks and along the apertures or bores. A tube rolling repair technique including rolling the inside diameters of the nozzles was utilized to repair leaking 304 stainless steel control rod drive penetration nozzles of nuclear boiling water reactors at Big Rock Point, Mich., in 1979, Nuclenor, Spain, in 1981 and Nine Mile Point, N.Y., in 1984. A similar tube rolling repair technique was utilized to repair leaking 304 stainless steel instrument penetration nozzles of nuclear pressurized water reactors at Garigliano Plant, Italy, in 1966 and Oyster Creek, N.J., in 1974. It is also known to apply radially outwardly directed forces to the inside diameters of heat exchanger tubes to expand the tubes within apertures of tube sheets or baffle plates to prevent rattling or striking of the tubes against the tube sheets or baffle plates, and U.S. Pat. Nos. 4,586,249 to Costlow et al, 4,649,429 to Sinha et al, 4,649,493 to Costner et al, 5,027,507 to Nelson et al and 5,101,559 to Gelpi et al are illustrative of such procedures. Leaking or degraded heat exchanger tubes have also been repaired by inserting sleeves within the tubes and thereafter expanding portions of the sleeves to create an interference fit between the sleeves and the tubes. U.S. Pat. Nos. Re. 30,802 to Rogers, Jr., 4,448,343 to Kochka et al, 4,580,426 to Zafred, 4,592,577 to Ayres et al, 4,639,994 and 4,653,164 to Cooper, Jr. et al, 4,724,693 to Tedder, 4,779,445 to Rabe, 4,783,890 and 4,847,967 to Gaudin and 4,793,044 and 4,827,594 to Cartry et al are exemplary of various sleeving procedures for repairing heat exchanger tubes.